Gas turbine engines typically include a fan section, a compressor section, a combustor section and a turbine section. A fan section may drive air along a bypass flowpath while a compressor section may drive air along a core flowpath. In general, during operation, air is pressurized in the compressor section and is mixed with fuel and burned in the combustor section to generate hot combustion gases. The hot combustion gases flow through the turbine section, which extracts energy from the hot combustion gases to power the compressor section and other gas turbine engine loads. The compressor section typically includes low pressure and high pressure compressors, and the turbine section includes low pressure and high pressure turbines.
Gas turbine engines generally include one or more bearing systems that support rotation of various components relative to an engine static structure or engine case. Gas turbine engines may use oil for cooling and lubrication of the bearing systems. Lubrication systems, such as those used in aircraft gas turbine engines, supply lubricant to bearings, gears and other engine components that use lubrication. The lubricant, typically oil, cools the components and protects them from wear. A typical oil lubrication system includes conventional components such as an oil tank, pump, filter and oil supply conduits. Tubing and conduits of various types can be used to route fluids throughout an engine, for example. Various double wall tubes may be used for delivery and transport of fluids, such as oil. A double wall tube may have an outer passage formed between an inner tube and an outer tube. The inner tube and the outer tube may each carry a fluid, and it may be difficult to maintain separation of the fluids at the exit of a double wall tube. Further, engine oil tubes and fittings may be subjected to relatively high temperatures. Once subjected to excessive heating, oil may undergo coking. Oil coking may cause solid oil deposits to form within oil tubes, causing undesirable effects such as blocked passageways and filters.